how to lock doors on extra lot sims 3

Hi Everyone!

I've got a question...

I just bought an extra lot for my sim (sims 3) so she can has a home to live and another lot to keep her horses.

But I can't lock doors or gates on the extra lot. So when I put the horses in the meadow, they can just run out because I can't lock the gates to keep them in there...

The only option I get when I press the fence is "real estate" 

Does anyone know how I can lock doors on the real estate/extra lot?

Thanks =)